Try to get something similar to these and cut out around the metal protector. It prevents the legs from ever making contact. Stern is doing something similar on new pins they put out to prevent decal wrinkle.

ebay.com link: Bally Williams Stern Pinball Cabinet Decal Protectors

No don't do that. IMO the plastic pincab protector typically causes a larger area of wrinkle damage to the decal. I would email Terry from Pinball Life he was selling them but can't find them on his site anymore. Sometimes Terry can pull a rabbit out of a hat to help us pinheads find things like this give him a try.

If you are going to go with pincab protectors try putting a felt cutout between the pincab and the decal that should help a bit. Please do not screw in the pincab protectors as that is not how they were designed to be used and could cause more damage. Below is an example of felt cut outs:
ebay.com link: 4 PINBALL MACHINE LEG CABINET PROTECTOR PADS FOR ANY PIN GAME WITH METAL LEGS

Are all of the metal protectors the same (will the sterns fit any/most)? If so, you can get them at a stern distributor. Looks like in Canada it's:

Starburst Coin Mach.
Toronto 416-251-2122

Bracket # 535-0599-00
Screw # 237-5800-00 x 2 per bracket 

I'm pretty sure they are good idea bdaily.

Here you go, from Pinball Life: http://www.pinballlife.com/index.php?p=product&id=2711

Thanks Rum-Z a couple weeks ago I was looking and couldn't find them.

Go with these from pinball life they should make your life much easier going forward.

What about just using an exacto to cut precisely around the pin cab protector? Doesn't that work?

No the pincab protectors move around that is part of what causes the wrinkling in the first place the metal ones are anchored in and don't move. Also, when you are redoing a cabinet decal it is not a good idea to cut out a large pincab protector size section of the decal. Not everyone uses pincabs in fact they are kind of losing traction as the metal protectors that are invisable and totaly prevent contact of the leg and cabinet work much better at preventing damage/wrinkling.

nice work on the backbox.
belle job, starburst a montreal doit etre capable de t'avoir ça.
sinon pinball life est un exellent choix.

Honestly pin can protectors are not needed for new or restored cabinets.

I like and the pin cab protectors but I use them to either cover existing damage or just to add a nice color contrast. Yellow ones look great on my acdc premium and tspp and green on wcs (wish they made purple). I also am a little ocd and if some of my games had them and others didnt it would bother me (enough to buy them and install them). I also have the same problem with stern flipper protector side rails. Bought some for tspp just to match hulk and acdc and met LE lol. Now just gotta find someone to powder coat them nuclear green.

I have pincabs installed on all my new sterns and have not gotten any wrinkles on my decals last I checked. I do tend to baby my new games and don't shake and nudge them as hard as a lot of players do. If you are really aggressive then use the metal ones or felt. Also when using pin cabs you don't want to under or over tighten your leg bolts. If they are too lose this will cause to much play between the pin cab prot and the decal. Too tight can cause it to dig in. I guess the nice thing is if they do cause wrinkles at least they cover them up lol.